Aging of Meat

Maturation or aging is accompanied by morphological changes which primarily affect the cytoskeleton. Microexaminations show that the Z lines, which as cross structures (cf. 12.2.1) separate the individual sarcomeres in the muscle fibril, are broken up during aging. In addition, the fibrillar proteins titin and desmin are degraded. In comparison, the contractile proteins myosin and actin are stable. They are attacked only at temperatures above 25 °C. The connective tissue present outside the muscle cells also remains intact. 

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The use of proteases for modification of protein functionality is an ancient art. Originally, the enzymes were either endogenous to the food (e.g., aging of meat) or part of an added bio-system (e.g. microbial cultures in cheeses) (3). With increased knowledge of what enzymes are and how they work, their delibrate isolation and addition to food systems became widely practiced. 

Lysosomes are involved in a great variety of catabolic activities. The machinery for autolysis of animal tissue apparently resides in the lysosomal particle. Lysosomal enzymes are capable of the complete hydrolysis of proteins to amino acids (59). The hydrolytic reactions of lysosomal enzymes have been implicated in tenderization during the aging of meat (31, 47, 60-66). 

The importance of muscle lysosomal enzymes to the food scientist stems from their apparent involvement in the aging of meats. For example, lysosomal cathepsins are possibly involved in the proteolytic degradation of muscle proteins (31). Lysosomal enzymes exhibit latency that is, they are retained in the lysosomal particle and released only when the particle membrane is damaged. In this regard the lysosomal enzymes are liberated and activated when the particle membranes are weakened by the postmortem drop in pH. Also, lysosomes are very subject to cryoinjury (72), and freezing and thawing of tissues such as muscle releases lysosomal enzymes resulting in autolysis. 

It is reported that cathepsins B, D and L degrade myofibrillar proteins, while cathepsin H scarcely causes hydrolysis of these proteins (22,23), SDS-PAGE analyses show that a polypeptide with a molecular mass of 30 kDa is produced during the postmortem aging of meat (24-28), This was shown to be derived from a myofibrillar protein, troponin T. The peptide (APPPPAEVPEVHEEV) derived from troponin T is also reported to increase during the storage of beef (29). 

From these results, it might be concluded that both m- and m-calpains and cathepsins B and L are responsible for the increase in peptides concentrations at the ultimate pH (5.5-5.8) during postmortem aging of meat. 

Figure 6. Medianism involved in the increase in peptides and free amino acids during the postmortem aging of meats. (Reproduced with permission from Nishimura (1998))...

Tenderness. The contractile state of the muscle after rigor mortis is a major factor in meat tenderness, which is affected by post-mortem conditions creating differences in tenderness. Ageing of fresh pork can be used to improve tenderness. The process is based on a continuous weakening of the structural elements by different endogenous muscle peptidases along with an improved palatability (Taylor et al., 1995). 

Such acid and calcium excretion may be important in development of osteoporosis. To test diets of meat and vegetable protein upon urinary acid and calcium, nine human adults, aged 22 to 69 years, were fed isonitrogenous diets of chicken or soy beans in seven-day feeding periods. Diets provided daily ... 

Relationship of Meat Consumption to the Age-Standardized Relative Risk of Death From Coronary Disease and All Other Causes Among California Adventist Men age 35-64,... 

Tikk, M. Tikk, K. T0rngren, M. A. Meinert, L. Aaslyng, M. D. Karlsson, A. H. Andersen, H. J. Development of Inosine Monophosphate and Its Degradation Products during Aging of Pork of Different Qualities in Relation to Basic Taste and Retronasal Flavor Perception of the Meat. J. Agric. Food Chem. 2006, 54, 7769-1711. 

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